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05-14-2022, 08:56 AM - 2 Likes   #46
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QuoteOriginally posted by jspi Quote
I don't consider myself a beginner, more of an intermediate but I feel this is a question I should have grasped (memorized?) long ago. If I'm wrong on any of my information, feel free to educate me.


1 stop of adjustment is either halving or doubling the amount of light hitting the sensor. This can be done by adjusting the shutter speed or aperture. Increasing the sensitivity of the sensor (ISO) doesn't increase the amount of light but has the same effect (although it does increase noise).


Let's say I'm taking a photo at f8, 1/640s, and ISO 6400 but it's "1 stop" too dark.

I could increase ISO to 12,800 (1 stop) but it'll have more noise than I like.

Or I could slow the shutter speed to 1/320s (1 stop) but the action will be blurry.

So I must adjust the aperture. Going with halving/doubling to adjust one stop, the aperture would be f4 but I believe that would be closer to 2 stops.

I understand the math behind 1 stop of aperture but I can't calculate that on the fly. My assumption is I need to memorize which f stops are one full stop from the one below/above (I've been refusing to do that). But I though I'd ask if there's a quick way to figure it out without having to memorize a chart. For now, I just assume f8 to f4 is 2 stops so f6.3 is probably close to one stop? f4 to f2 is likely 2 stops so f4 to f3.2 is probably 1 stop. Assume... Probably... Just set to M, look at the expose meter, and hope it's close. Yeah, there's a bit of guessing and I'm most likely wrong but I have a big SD card so I'm faking my way to descent photos... Although a bit of memorization would be a small price to pay for throwing away less photos. Not to mention the extra time I'd have to be more creative while framing shots.
Your math is perfect up to the point of aperture.

Aperture is the ratio of focal length over diameter. When you double or halve the aperture number, you are changing the area of the opening by 1/4 or 4 respectively because area is proportional to the square of the diameter.

That’s why the the f-stops are numbered 1.4 - 2.0 - 2.8 - 4.0 - 5.6 - 8 etc…. So to change the aperture by 1 stop you need to change it by multiplying/divide the aperture by the square root of 2, or 1.4

The reason these odd aperture numbers are important is that for any lens the light projected per square area is constant for the same aperture value.

05-17-2022, 07:50 AM   #47
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The mathematical progression is just powers of the square root of 2 rounded to two significant digits. Even powers are whole numbers: 1, 2, 4, 8, 16, 32… Odd powers are multiplied by sqrt(2), with 1.4 being a useful approximation: 1.4, 2.8, 5.6, 11, 22…

You can verify this yourself with any calculator capable of square roots, though a scientific calculator might make it more obvious. If you have an iPhone, launch the calculator and rotate your device in landscape mode and it’ll switch to scientific mode.
05-17-2022, 08:03 AM   #48
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QuoteOriginally posted by jspi Quote
I don't consider myself a beginner, more of an intermediate but I feel this is a question I should have grasped (memorized?) long ago. If I'm wrong on any of my information, feel free to educate me.


1 stop of adjustment is either halving or doubling the amount of light hitting the sensor. This can be done by adjusting the shutter speed or aperture. Increasing the sensitivity of the sensor (ISO) doesn't increase the amount of light but has the same effect (although it does increase noise).


Let's say I'm taking a photo at f8, 1/640s, and ISO 6400 but it's "1 stop" too dark.

I could increase ISO to 12,800 (1 stop) but it'll have more noise than I like.

Or I could slow the shutter speed to 1/320s (1 stop) but the action will be blurry.

So I must adjust the aperture. Going with halving/doubling to adjust one stop, the aperture would be f4 but I believe that would be closer to 2 stops.

I understand the math behind 1 stop of aperture but I can't calculate that on the fly. My assumption is I need to memorize which f stops are one full stop from the one below/above (I've been refusing to do that). But I though I'd ask if there's a quick way to figure it out without having to memorize a chart. For now, I just assume f8 to f4 is 2 stops so f6.3 is probably close to one stop? f4 to f2 is likely 2 stops so f4 to f3.2 is probably 1 stop. Assume... Probably... Just set to M, look at the expose meter, and hope it's close. Yeah, there's a bit of guessing and I'm most likely wrong but I have a big SD card so I'm faking my way to descent photos... Although a bit of memorization would be a small price to pay for throwing away less photos. Not to mention the extra time I'd have to be more creative while framing shots.
If you were to actually calculate the areas of the apertures of the different numbered stops (f8, f11, etc.) you would find out that the area from one "full stop" to the next is either 1/2 or double (f11 is 1/2 the area of an opening as f8, which is 1/2 the area of 5.6, etc.). This is all based on the focal length of a lens, so an f1 50mm lens would have an aperture opening of 50mm. Given that each one stop change means the opening has been cut in half or doubled, then that also means that the amount of light has also been cut in half or doubled. SO f8 lets in twice as much light as f11, etc.

f stops work in conjunction with the shutter speeds, which will also cut in half or double the amount of light at the standard shutter speeds (1/60/sec lets in about twice the light as 1/125/sec). ISO works the same way, with ISO 100 needing twice the light as ISO 200 to give the same exposure. The DIN system, common in Europe, uses log changes, so DIN 21 (ISO 100) needs twice the light as DIN 24 (ISO 200). 3 is a natural log change. Doubling or halving the light is a logarithmic change, so these systems all work nicely.

In review then, f11 @ 1/30 sec gives the same amount of light to the sensor/film as f8 @ 1/60 sec, and 1/15sec @ f16, and so on (all for a given ISO, say ISO 100). f11@ 1/30 sec at ISO 100 is the same exposure as f16 @ 1/30 sec at ISO 200 OR f11 @ 1/60 sec at ISO 200. Depth of field does not play into the exposure calculations, only the compositional preferences of the photographer.

Last edited by BigDave; 05-17-2022 at 08:09 AM.
05-17-2022, 08:05 AM   #49
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If you're not printing you will never learn the difference between stops.

05-17-2022, 08:08 AM   #50
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QuoteOriginally posted by que es tu Quote
Cool! Thank you!!
Another thing to keep in mind, with memorizing f stops. Just remember two of them, f4 and f 5.6. Then you double every other one (or half going down) so f4, f5.6, f8 (double 4), f11.2 (the actual f stop, double 5.6), f16, f22.4 (rounded to 22), f32 and f45 (actually 44.8, rounded to 45). Going down from f4 gives f2.8 (half of 5.6), f2, f1.4 and then f1 (a very rare bird!).
05-17-2022, 08:41 AM   #51
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To avoid all of the semantics and supposed technicalities I simply say I stop it down
05-17-2022, 09:29 AM   #52
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QuoteOriginally posted by jspi Quote
I don't consider myself a beginner, more of an intermediate but I feel this is a question I should have grasped (memorized?) long ago. If I'm wrong on any of my information, feel free to educate me.


1 stop of adjustment is either halving or doubling the amount of light hitting the sensor. This can be done by adjusting the shutter speed or aperture. Increasing the sensitivity of the sensor (ISO) doesn't increase the amount of light but has the same effect (although it does increase noise).


Let's say I'm taking a photo at f8, 1/640s, and ISO 6400 but it's "1 stop" too dark.

I could increase ISO to 12,800 (1 stop) but it'll have more noise than I like.

Or I could slow the shutter speed to 1/320s (1 stop) but the action will be blurry.

So I must adjust the aperture. Going with halving/doubling to adjust one stop, the aperture would be f4 but I believe that would be closer to 2 stops.

I understand the math behind 1 stop of aperture but I can't calculate that on the fly. My assumption is I need to memorize which f stops are one full stop from the one below/above (I've been refusing to do that). But I though I'd ask if there's a quick way to figure it out without having to memorize a chart. For now, I just assume f8 to f4 is 2 stops so f6.3 is probably close to one stop? f4 to f2 is likely 2 stops so f4 to f3.2 is probably 1 stop. Assume... Probably... Just set to M, look at the expose meter, and hope it's close. Yeah, there's a bit of guessing and I'm most likely wrong but I have a big SD card so I'm faking my way to descent photos... Although a bit of memorization would be a small price to pay for throwing away less photos. Not to mention the extra time I'd have to be more creative while framing shots.

Hi, sorry to be pedantic but the "f" number is actually the reciprical of the lenses focal length. So for a 100mm lens f2 means that the diameter of the aperture is 1/2 x 100mm = 50mm. f8 Is 1/8 x 100 = 12.5mm.

In most cases the f stops on a lens are normally one stop up or down and is a general guide and could be swapped with one step in shutter speed.

I do hope that helps a little. 😀

05-17-2022, 09:59 AM   #53
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QuoteOriginally posted by que es tu Quote
I think rote memorization is tedious, but the best way to learn the f stop progression. I got a little notebook and wrote out the f stops from f1.4 to f64 and memorized them while I walked the dog each day! I use half stops as they are easier for me to remember and understand, plus I can get where I want to be faster. I tried but gave up memorizing the shutter speeds as I predominantly shoot in Av and keep the minimum speed in mind.
Having actually earned a degree in mathematics, I agree that rote memorization is “tedious”.
I find it easier to remember the first two steps - “1” and “1.4”, then multiply repeatedly by 2 to get the others.
Actually, my camera remembers for me.
05-17-2022, 10:26 AM   #54
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QuoteOriginally posted by jspi Quote
I don't consider myself a beginner, more of an intermediate but I feel this is a question I should have grasped (memorized?) long ago. If I'm wrong on any of my information, feel free to educate me.


1 stop of adjustment is either halving or doubling the amount of light hitting the sensor. This can be done by adjusting the shutter speed or aperture. Increasing the sensitivity of the sensor (ISO) doesn't increase the amount of light but has the same effect (although it does increase noise).


Let's say I'm taking a photo at f8, 1/640s, and ISO 6400 but it's "1 stop" too dark.

I could increase ISO to 12,800 (1 stop) but it'll have more noise than I like.

Or I could slow the shutter speed to 1/320s (1 stop) but the action will be blurry.

So I must adjust the aperture. Going with halving/doubling to adjust one stop, the aperture would be f4 but I believe that would be closer to 2 stops.

I understand the math behind 1 stop of aperture but I can't calculate that on the fly. My assumption is I need to memorize which f stops are one full stop from the one below/above (I've been refusing to do that). But I though I'd ask if there's a quick way to figure it out without having to memorize a chart. For now, I just assume f8 to f4 is 2 stops so f6.3 is probably close to one stop? f4 to f2 is likely 2 stops so f4 to f3.2 is probably 1 stop. Assume... Probably... Just set to M, look at the expose meter, and hope it's close. Yeah, there's a bit of guessing and I'm most likely wrong but I have a big SD card so I'm faking my way to descent photos... Although a bit of memorization would be a small price to pay for throwing away less photos. Not to mention the extra time I'd have to be more creative while framing shots.
The chart of aperture and itīs relation sqrt(2) has been dealt with. Thatīs great.
What I like about your original post is the description of the relations of tradeoffs.
With a modern digital camera you donīt really need to care about proper exposure.
But you need to know about the tradeoffs!
I met somebody on the Newcastle-Amsterdam ferry just yesterday.
We were both shooting the sunset. (I know)
And then I found out he always shoots ISO 25600. "That way I donīt have to care."
Yeah, right.
05-17-2022, 12:37 PM   #55
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QuoteOriginally posted by Teefus Quote
In most cases the f stops on a lens are normally one stop up or down and is a general guide and could be swapped with one step in shutter speed.
The classic manual lenses such as the Pentax M-Series of the 1980's mostly had aperture indents (ie clicks) at half-stop intervals, and I believe other brands were the same. Only near the ends of the range did they tend to be a whole stop apart. At the smallest apertures there is only a small mechanical difference between the stops, and I guess the thinking with regard to the larger apertures is that you are are going that far you might as well go all the way.
QuoteOriginally posted by reh321 Quote
I find it easier to remember the first two steps - “1” and “1.4”, then multiply repeatedly by 2 to get the others.
I learned the sequence at my father's knee, he was a semi-pro. He gave me an old 35mm in my early teens (no exposure meter then) and I used it mostly for sunny snaps, so for years I used only a few settings, maybe f5.6 - f16, not much to remember. Later I learned to extend from either end of that core range. You are right to make the point that the universally preferred stop values have "1" as the origin. Even though very few lenses have ever been made with an f1 setting, the conventionally engraved (or electronically indicated) preferred values are as if there was an f1 setting as the start point.
05-17-2022, 12:42 PM - 1 Like   #56
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QuoteOriginally posted by MHildebrandt Quote
And then I found out he always shoots ISO 25600. "That way I donīt have to care."
.
Still better than always shooting with the lens cap on. but with the lens cap on I don't have to worry about any of it. FL, shutter speed, battery, card, focus, no worries. Even less if I leave the camera at home. It won't get damaged, lost, or stolen.
05-17-2022, 01:29 PM   #57
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QuoteOriginally posted by MHildebrandt Quote
The chart of aperture and itīs relation sqrt(2) has been dealt with. Thatīs great.
What I like about your original post is the description of the relations of tradeoffs.
With a modern digital camera you donīt really need to care about proper exposure.
But you need to know about the tradeoffs!
I met somebody on the Newcastle-Amsterdam ferry just yesterday.
We were both shooting the sunset. (I know)
And then I found out he always shoots ISO 25600. "That way I donīt have to care."
Yeah, right.
Wow. I guess he only needs a couple of stops of dynamic range then. Sheesh.
05-17-2022, 06:06 PM   #58
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exposure stops

Back in the pre-digital days, Eastman Kodak used to sell pocket cards that worked like slide rules for determining the proper exposures for various lighting situations. If you could find one of those, perhaps from an older photographer, it would be a big help to you. Keep in mind that f/8 on a 28mm lens is not the same size opening as f/8 on an 85mm lens (assuming that both lenses have the same size mount) because the f/stop is a ratio of the size of the lens opening (the aperture) to the distance from the optical center of the lens to the film or digital sensor and the different lenses have optical centers at different points. In fact, if you look at either lens set to f/8 (or any other stop) from the back and then from the front, it will appear that the stop has changed sizes! This is an optical illusion produced by the different levels of magnification in the different lens elements.
And if that isn't confusing enough, if you could hop into the wayback machine and travel back in time to watch Matthew Brady at work photographing the civil war, you might notice that his lenses didn't have internal iris mechanisms so lens openings had to be set by sliding a metal card with a certain size opening that would slide into a slot in the top of the lens so that the correct lens opening would appear at the optical center of the lens. These openings were called T/Stops and were more accurate than todays f/stops but not so much so that the slight loss of precision couldn't be replaced by the convenience of an adjustable in-lens system like we have today.
05-18-2022, 01:42 AM   #59
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QuoteOriginally posted by Don Heath Quote
Eastman Kodak used to sell pocket cards that worked like slide rules for determining the proper exposures for various lighting situations. If you could find one of those, perhaps from an older photographer, it would be a big help to you.
There are loads of exposure calculators on Ebay, except they are usually made of plastic. Should cost no more than Ģ5. I used one of these, still have it somewhere.


05-18-2022, 06:19 AM   #60
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Showing up late to this party and I see lots of very good explanations and tips. If this were for film cameras I wouldn't have much to say as the little instamatic 126 or 110 cameras(or that awful disc one) I used had no controls.

Unless I'm in extreme conditions like night sky or astrophotography(AP), I usually prefer to let the camera sort out the best combination of exposure and iso within the limits I set, usually 100-800 on my k50 and k5, and set the dial to "A" aperture mode, which lets me use the iris to set depth of field as needed for the shot, while letting the computer figure out the hard stuff. I also use the exposure offset in tougher light conditions like winter time low sun. You can preview the result with the manual iris button or post shot previews if the action doesn't allow setup time. Low light or indoors usually requires a bit more compromise but this setup has served me well most of the time.

I consider my digital cameras to be computer instruments, like all my other tech. By researching the sensor and experimenting with raw output long exposure shots at different iso/gain settings that the imx071 sensor used in the k5 and k50 that lower gain has better dynamic range and less noise and that given a fixed(ground subjects) or tracking(night sky) mount, I found that longer exposures at lower iso worked better with less noise and better colors than combining(stacking) more shots at high gain and shorter exposures. While this doesn't translate directly to daytime photography, which often doesn't allow for a tripod, it did show me that it's easier to not introduce error/noise in the photo than it is to fix it once it's there.

My takeaway from this thread is the realization that I too have been needlessly wearing out my encoders(knobs) with 1/3 stops. :P

Last edited by blues_hawk; 05-18-2022 at 06:24 AM. Reason: thought process...
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